The welding of aluminum articles requires specialized processes to provide high quality weldments. More particularly, a welded joint between aluminum articles must possess strength and ductility. Strength is needed to hold the welded joint together, and ductility is necessary to permit plastic deformation without fracture. Strength and ductility are effected by four major factors: alloy composition, oxide contamination, porosity, and weld penetration.
In the prior art, articles made of metals other than aluminum are generally lubricated with mineral oil compositions before they are press-fitted together. The fitted articles can then be welded satisfactorily to form a unitary weldment.
When aluminum parts are to be welded, they must be thoroughly cleaned to remove all traces of lubricants in order to avoid hydrogen porosity problems caused by the lubricant. However, if forming or mating operations such as press-fitting are required prior to welding, both mating parts are traditionally cleaned and assembled in the as-cleaned condition in order to avoid interference by a lubricant with the subsequent welding operation. When a interference fit is required, this causes galling and scratching of the parts. Consequently, procedures such as heat-fitting and shrinkage-fitting are commonly employed.
It is a principal objective of the present invention to provide a process for press-fitting together aluminum articles which must subsequently be welded, wherein the articles are lubricated with a dispersion of colloidal graphite prior to press-fitting.
A related object of the present invention is to provide a lubricant composition that avoids hydrogen porosity in welded joints of aluminum articles which are press-fitted together and subsequently welded.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following detailed description.